<template>
  <div>
      <ul class="list">
          <li class="item" v-for="item of letters " 
          :key="item"
          :ref="item"
          @click="handleLetterClick"
          @touchstart = "handleTouchStart"
          @touchmove = "handleTouchMove"
          @touchend = "handleTouchEnd"
          >{{item}}</li>
      </ul>
  </div>
</template>

<script>
export default {
    name:'Alphabet',
    props: {
      cities: Object
    },
    computed: {
      letters() {
        const letters = []
        for (let i in this.cities) {
          letters.push(i)
        }
        return letters
      }
    },
    data () {
      return {
        touchStatus:false,
        startY:0,
        timer:null
      }
    },
    updated () {
     this.startY = this.$refs['A'][0].offsetTop
    },
    methods: {
      handleLetterClick (e) {
        // debugger
        // console.log(e.target.innerHTML);
      this.$emit('change', e.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          const touchY = e.touches[0].clientY - 79
          const index = Math.floor((touchY - this.startY) / 20)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change', this.letters[index])
          }
        }, 16)
      }
    },
    handleTouchEnd () {
        this.touchStatus = false
    }
  }
}
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list
    display:flex
    justify-content:center
    flex-direction:column
    position:absolute
    top:1.58rem
    right:0
    bottom:0
    width:.4rem
    .item
        line-height .4rem
        text-align:center
        color:$bgColor
</style>